Apparatus for removing metal oxide scale from a reactor wall



Dec. 29, i 1970 D. E. DARR A APPARATUS FOR REMOVING METAL OXIDE SCALEFROM A REACTOR WALL 4 Sheets-Sheet 1 Original Filed July 2, 1964 4 A i"J n) ,5 IIIY 3 J I no a 1 N 3 4 L. r 0 /0,// 2 l o m ON. 0 r A l m a Ki l 3 A A .K 4 W I l\ M FIG-I Dec. 29, 1970 D. E. DARR ET AL 3,550,177APPARATUS FOR REMOVING METAL OXIDE SCALE FROM A REACTOR WALL OriginalFiled July 2, 1964 'IIIIIII], I a

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ATrom/anr United States Patent O 3,550,177 APPARATUS FOR REMOVING METALOXIDE SCALE FROM A REACTOR WALL Donald E. Darr, Wadsworth, Ohio, RogerS. Leiser,

Decatur, Ill., and Clifford E. Loehr, Akron, and Kenneth W. Richardson,Barberton, Ohio, assignors to PPG Industries, Inc., Pittsburgh, Pa., acorporation of Pennsylvania Original application July 2, 1964, Ser. No.379,825, now Patent No. 3,423,186, dated Jan. 21, 1969. Divided and thisapplication Aug. 15, 1968, Ser. No. 753,014

Int. Cl. B08b 9/08 US. Cl. -1041 14 Claims ABSTRACT OF THE DISCLOSUREThe preparation of metal oxide, e.g., titanium dioxide, by vapor phaseoxidation of metal halide, e.g., titanium tetrahalide, is described.Diificulties in maintaining reactor operation because of metal oxidescale buildup within the reactor is discussed. Method and apparatus areproposed for eliminating such ditficulties.

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a divisionof application Ser. No. 379,825, filed July 2, 1964, in the names ofDonald E. Darr, Roger S. Leiser, Clifford E. Loehr, and Kenneth W.Richardson, now US. Pat. 3,423,186.

BACKGROUND OF THE INVENTION In the typical vapor phase oxidation processfor the production of titanium dioxide, titanium tetrahalide, and anoxygenating gas, e.g., oxygen or oxygen-containing gas, are introducedinto a closed reaction chamber either in the presence or absence of afluidized bed, the chamber preferably maintained at a temperature above600 C. in a range of about 850 to 1700 C. Typical processes aredisclosed in US. Letters Patents 2,653,078 to Lane; 2,750,260 to Nelsonet al.; 2,791,490 to Willcox; 2,670,- 275 to Olson et al.; 2,823,982 toSaladin et al.; 2,968,529 to Wilson; 2,989,509 to Frey; 3,068,113 toStrain et al.; 3,069,281 to Wilson; and 3,069,282 to Allen.

The metal halide, e.g., titanium tetrachloride, is preferably introducedinto the reaction chamber or reactor in a vapor state and is oxidized byoxygen or oxygen-containing gas such that titanium dioxide is formed.

The walls of the oxidation reaction chamber are preferably constructedout of a zirconium base brick, ceramic, or other suitable material. Afrequent problem encountered in the production of titanium dioxide isthe formation of a metal oxide growth or encrustation upon the walls ofthe reaction chamber. If this encrustation or metal oxide formation andbuildup is not timely removed,

it develops into a donut or ring which eventually closes up and plugsthe reactor, thereby hindering the continuous and economical operationof a TiO vapor phase oxidation process and making the processimpractical as a commercial operation.

In the prior art, several methods have been proposed for removing themetal oxide accumulation. Thus, it has been proposed to flow a gastransversely through the reactor walls. See, for example, US. LettersPatent 2,957,- 753. Us. Letters Patent 2,805,921, issued to Schaumann(also note British specification 822,910) teaches the dislodging of thescale by means of an internally cooled cutting element. The reactorwalls also may be cleaned via sonic vibrators. It has also been taughtthat oxide scale buildup may be prevented by diffusion of inert gasesthrough porous metal walls. Belgian Pat. No. 640,553 teaches the flexingof the reactor Walls as a means of removing oxide growth.

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BRIEF SUMMARY OF THE INVENTION This invention relates to a novel methodand apparatus to be used in conjunction with the oxidation of a metalhalide to produce metal oxide. More particularly, it relates to a methodand apparatus to be used in the production of titanium oxide by thevapor phase oxidation of titanium tetrahalide, e.g., titaniumtetrachloride, titanium tetrabromide, and titanium tetraiodide.

In the practice of the present invention, the metal oxide scale buildupis continuously removed and further buildup prevented by passing one ormore solid ceramic or lava edges immediately adjacent to the surface ofthe reactor wall, such that each solid ceramic edge brushingly contactsand displaces the metal oxide accumulation.

In one embodiment, the solid ceramic edges are arranged in a circular orring-like fashion about the reactor axis and moved to and fro, that is,reciprocated upwardly and downwardly, in a direction parallel to thereactor axis.

In a preferred embodiment, the ceramic edges are positioned as arms orstrips parallel to the reactor axis and moved in a circumferentialdirection along the reactor wall about the axis.

Likewise, in the preferred practice of this invention, it is preferredthat the solid ceramic dedusting members or edges be supported andretained in the predetermined position by means of support membersthereby increasing the over-all section modulus. Such support membersare particularly desirable where one or more ceramic arms are projectedupwardly from the bottom of the reactor in cantilever fashion along thereactor walls, that is, in a direction parallel to the reactor axis.

Although the supports may be constructed out of ceramic material, it ispreferred to employ a material that Will provide high strength perpound, particularly at the elevated temperature conditions within thereactor. It has been found that a suitable material is nickel formed orshaped as tubular or pipe-like elements and through which there iscirculated a cooling heat transfer fluid.

Although the supports may be constructed out of a metal material asnoted above, it is essential that the brushing or dedusting arms beconstructed out of ceramic since metallic materials abrade and quicklywear away, particularly at the edge such that there results a flattenededge which tends to compact the metal oxide onto the wall surface ratherthan remove it. However, when ceramic is employed, the solid edge memberretains its shape and thus continues to perform its brushing anddedusting function over a prolonged period.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood by reference to the drawings and the figures thereon.

FIG. 1 represents a three-dimensional view of one preferred practice ofthe present invention.

FIG. 2 represents a cross-section through FIG. 1 through a plane justbelow the caps 7, 7A, and 7B, parallel to the reactor bottom 12.

FIG. 3 represents a modification of FIG. 1 wherein only one ceramicdeduster arm is employed.

FIG. 4 represents a three-dimensional view of a further practice of thepresent invention.

FIG. 5 is a plan view of FIG. 4.

FIG. 6 represents a three-dimensional view of a ceramic dedusting arm.

FIG. 7 represents a plan view of FIG. 6.

FIG. 8 represents a plan view of a modification in the geometric shapeof the ceramic dedusting arm.

FIGS. 9 and 10 represent cross-sectional views of various reactor shapesand also show schematically the positioning of a ceramic arm within eachreactor.

A 3 FIG. 11 represents a top portion of a reactor with a concentric tubearrangement by which reactants are introduced.

DETAILED DESCRIPTION FIG. 1 represents an over-all three-dimensionalview of one preferred embodiment of the present invention. FIG. 2 is aplan view of FIG. 1.

More particularly, there is shown in part a cylindrical metal oxidereactor wall 13 and a bottom 12 with axial shaft 2 and concentricconduits 1 and 11 projecting upwardly through the center of bottom 12.

A cooling fluid is introduced from a source (not shown) into inletconduit 1 and is flowed upwardly about the shaft 2. At or near the topof conduit 1, the fluid stream splits and flows into support conduits 3,4, 5, 3A, 4A, 5A, 3B, 4B, and 5B, each of which is connected to andprojects from conduit 1 at an angle, e.g., 90, and then curves upwardly,e.g., by means of an elbow in a direction substantially parallel to theprojected common axis of the shaft and conduits l and 11.

Ceramic dedusting arm 6 is held and maintained in a predeterminedposition in between support conduits 4 and 5 as shown. Similarly, eachpair of support conduits 4A and 5A, 4B and 5B, retains and supportsrespectively a ceramic dedusting arm 6A and 68 as shown in FIG. 2.

In addition, support conduits 3, 4, and 5 support and retain centerreturn conduit 8 in a predetermined position. Similarly, conduits 3A,4A, and 5A retain return conduit 8A and conduits 3B, 4B, and 5B retainreturn conduit 88. Return conduits 8, 8A, and 8B are preferablyflattened to an eliptical shape as shown in the FIGS. 1 and 2. Tubes 3,4, 5, 3A, 4A, 5A, 3B, 4B, and 58 also may be flattened to an elipticalshape.

At the top of center return conduit 8, there is atfixed a cap 7 whichprovides a common closed chamber for conduits 3, 4, 5, and 8. Similarly,cap 7A is aflixed to conduits 8A and cap 7B is aflixed to conduit 8B,thereby providing common chambers, respectively, for conduits 3A, 4A,5A, 8A, and 3B, 4B, 5B, and 8B.

Internally of each conduit 8, 8A, and 8B, there is provided,respectively, baflle means 9, 9A, and 9B.

Conduit 8 is then joined by connecting conduit 10 to conduit 83, theconduit 10 being connected and joined to conduit 8 at a point abovebaflle 9 and to conduit 88 at a point below baflie 9B.

Similarly, conduit 8B is connected to 8A by means of 10B, which joins SEat a point above 9B and 8A at a point below 9A.

Finally, conduit 8A is connected to 8 by 10A which connects 8A at apoint above baflie 9A and 8 at a point below bafile 9.

Thus, in the operation of the novel dedusting apparatus hereinbeforedescribed, a cooling fluid flows into and upwardly through conduits 3,4, 5, 3A, 4A, 5A, 3B, 4B, and 5B.

The fluid flows out of the upward ends of conduits 3, 4, and 5 into thechamber provided by cap 7 and then downwardly through center returnconduit 8 to baflie 9, and then through connecting conduit 10 to returnconduit 8B (at a point below baflle 9B). The fluid then continues itsflow downwardly in conduit 8B to exit conduit 11 which is connected toan appropriate reservoir (not shown).

Simultaneously, fluid in conduit tubes 3B, 4B, and 5B flows into thechamber of cap 7B, downwardly through center conduit SE to baflie 9B,through connecting tube 10B to center conduit 8A (below baflie 9A) anddownwardly into conduit 11.

Likewise, fluid in conduit tubes 3A, 4A, 5A flows into the chamber ofcap 7A, downwardly through center conduit 8A to baflie 9A, throughconnecting tube 10A to center conduit 8, and downwardly in tube 8 toconduit 11.

Simultaneously, the entire assembly is rotated by shaft 2 which isconnected to any appropriate or conventional drive means (not shown),and as the assembly turns, the ceramic scraping arms or elements contactand brush accumulated metal oxide from the reactor wall 13. The coolingfluid flowing in tube 1 helps to cool the shaft 2 and also protects itfrom the hot fluid exiting through tube 11.

Although FIGS. 1 and 2 illustrate the use of three ceramic arms, it isto be understood that additional arms may be added by one skilled in theart. Likewise, it is possible to employ less than three arms, e.g., onearm such as shown in FIG. 3.

The embodiment of FIG. 1 can be operated without the use of bafiies 9,9A, and 9B and connecting conduits 10, 10A, and 10B, such that thecooling fluid flow through the supports of each arm is independent ofthe flow in every other arm. However, when such a system is employed, anunequal pressure drop and temperature regulation results and hot spotscan occur with bumout in one or more supports unless the flow conditionsin each arm are balanced.

FIG. 3 represents a modification of FIG. 1 wherein there is providedonly one arm 6 with only one series of supports 3, 4, 5, and 8. Thelower or bottom portions of tubes 3, 4, 5, and 8 are not shown in FIG. 3but are connected to tubes 1 and 11 the same as illustrated in FIG. 1.Balfle 9 as shown in FIG. 1 is removed such that the cooling fluid fromsupport tubes 3, 4, 5, is returned directly to conduit 11 by means ofreturn tube 8.

Since only one arm '6 is provided, the cantilever effect in FIG. 3 ismore pronounced than in FIG. 1; and, accordingly, it may be preferred touniformly and gradually increase the section modulus of the arm 6 and/orsupports 3, 4, 5, and '8 in a direction toward the reactor bottom 12.

Although FIGS. 1, 2, and 3 illustrate the use of four tubes, e.g., 3, 4,5, and 8, it will be obvious to one skilled in the art that fewer ormore support tubes may be employed.

FIG. 4 represents a further modification. More particularly, there isshown three arms 6, 6A, and 6B with ring supports 20 and radial supports21 connected to a central axial support 11.

In a preferred arrangement, the supports are tubes through which thereis circulated a cooling fluid which is from a source (not shown) toaxial tube 11. At the top of tube 11 there is shown a further tube 22with downwardly projecting nozzles 23 from which the circulated fluid isdischarged into the interior of the reactor 13.

FIGS. 6 and 7 illustrate a three-dimensional and a plan view,respectively, of a ceramic dedusting arm. More particularly, there isshown a ceramic arm 60 having two sides, 61 and 62, at an exterior angletheta 6. Also, there is shown side 63 at an interior angle phi to side61, such that sides 61 and 63 project to a ceramic dusting edge 64. Thebroken line 65 represents a tangent to the reactor wall 13 at theprojected contact of the point 64 to the wall, the side 61 being at anangle alpha 0: to the tangent 65.

FIG. 8 is a plan view of a modification of the ceramic arm of FIG. 6.There is shown a ceramic arm having sides 81 and 83 forming a point 84with an angle phi between the two sides, and a side 82 at an angle theta6 to the side 81. The broken line 85 represents a tangent to the reactorwall 13 at the projected contact of the point 84 to the wall 13, theside 81 being at an angle alpha 1x to the tangent 85. There is alsoshown in FIG. 8 a hole 86 in the body of the arm through which there maybe inserted a support rod for the arm. Such a support rod would not haveto be resistant to corrosion, e.g., from chlorine and/or oxygen, sincethe ceramic arm would serve as a protective layer. However, the metalwould have to retain a reasonable tensile strength at elevatedtemperatures, e.g., at about 1600= F. Such metals would include, forexample, alloys of iron, carbon, titanium,

zirconium, hafnium, vanadium, tungsten, nickel, and/or chromium.

FIG. 9 shows a reactor 92 having an inside wall 93 which is decreased indiameter by means of steps or corbels 94 and 95. As shown in the figure,there is provided a single ceramic arm 96 which follows the contour ofthe wall 93.

FIG. shows a reactor 102 having an inside wall 113 which uniformly andgradually decreases in diameter to a point 117. As shown in the figure,there is provided a single ceramic arm 116 which follows the contour ofthe wall 113.

FIG. 11 shows the top portion of a reactor 123 having an arrangement ofconcentric tubes for the introduction of reactants. More particularly,there is shown an inner tube 124 through which an oxygenating gas, e.g.,oxygen, N0 N0 H 0 is introduced into the reactor 123. There is alsoshown a tube 125 which is concentric to tube 124 whereby an annulus 129is formed. An inert gas is fed by means of tube 127 into annulus 129 andu then emitted from annulus 129 into the reactor 123. Preferably, tube127 is a wide-angle distribution tube as disclosed in copending US.application Ser. No. 360,937, filed Apr. 20, 1964, by Benner and Loehr.By inert gas it is meant any gas which is inert with respect to themetal halide and oxygenating reactants, for example, chlorine, argon,nitrogen, helium, krypton, xenon, carbon dioxide, or mixtures thereof.

External to tube 125, there is provided concentric tube 126 such thatannulus 130 is formed. Metal halide, preferably in a vaporous state, isintroduced through tube 128 into annlus 130, the halide then flowinginto reactor 123. Tube 128 is preferably a wide-angle distribution tube,the same as tube 127.

Where only one ceramic arm is employed, e.g., as disclosed in FIGS. 3,9, and 10, the arm is characteristically rotated about the insidecircumference of the reactor wall at a rate of /3 to 540 revolutions perhour, preferably 1% to 4 revolutions per minute, that is, at a preferredrate of about 80 to 250 feet of internal wall circumference per minutefor a reactor 14 feet in diameter. Where more than one arm is used, therate may be appropriately decreased by a factor equal to the totalnumber of ceramic arms employed.

As noted hereinbefore, it is essential that the dedusting arm be of aceramic material since other materials, particularly metals, wearquickly and cause the dedusting arm to become a compaction device andbend inwardly. Any ceramic material may be employed which has a thermalconductivity of less than 210 B.t.u./(hr.), (sq. ft.), F./inch),preferably less than 25, and a hardness of at least 5.0 on the Mohsscale (where talc equals 1.0 and and diamond equals 10.0). In addition,the ceramic should have suflicient resistance to a corrosiveenvironment, e.g., chlorine, at an elevated temperature of 1832 F.

A typical ceramic which is used in the practice of this invention is asteatite product of talc, such as 3MgO-4SiO -H O. Likewise, there may beused ceramic materials containing fused oxides such as alumina (A1 0zirconia (ZrO thoria (ThO beryllia (BeO), magnesia (MgO), apinel (MgAl Oforsterite (Mg SiO also, ceramic nitrides, such as silicon nitride,aluminum nitride, boron nitride, ferroelectric ceramics, such as bariumtitanate; or mixtures of same. Likewise, silicates, e.g., aluminumsilicate or magnesium silicate, may be used. In addition, there may beemployed ceramics containing CaSiO (wallastonite), Al (Si O (Ol-I)(pyrophyllite), Al SiO (sillimanite), Al Si O and Mg (Si O (OH), as wellas mixtures of same.

Typical compositions would include 78 percent by weight A1 0 and percentby weight SiO 81 to 85 percent by weight A1 0 and 14 to 16 percent byWeight SiO 70 percent by weight A1 0 and 92.5 percent by weight Z10 and5 percent by weight C210; and 97 percent by weight MgO and 2 percent byweight SiO Furthermore, the ceramic wall of the reactor is preferablyselected from the same or similar ceramic and lava materials.

If metal supports are provided as illustrated in FIGS. 1 to 5, it isdesirable that a cooling fluid be circulated internally of the supportsin order to keep the surface tem perature of the selected supportmaterial below the temperature at which the metal material corrodes,e.g., from attack by halides and/or halogen gases, particularlychlorine, and below the temperature at which the metal strength sharplydeclines. At lower temperatures, the tensile strength of the metal-likematerials is greater than at higher temperatures. Where the supports areconstructed out of nickel or a nickel alloy, the surface temperatureshould be maintained below the temperature at which chlorine or otherhalide will attack the metal, e.g., below 1000 F. for most nickelalloys, preferably, 500 to 700 F.

The surface temperature of the metal support is preferably controlled byregulating the volume per unit time of cooling fluid which is circulatedinternally of the support.

Where a support is provided internally of the arm, as illustrated inFIG. 8, such support may be a solid member since it will be protectedfrom corrosion by the surrounding ceramic arm.

Typical nickel alloys which may be employed are listed in the Handbookof Huntington Alloys, published by the Huntington Alloy ProductsDivision of the International Nickel Company, Inc., (first edition,March 1962), on pages 4 and 6, particularly Nickel 200 which consists of99.45 percent nickel, 0.06 percent carbon, 0.25 percent magnesium, 0.15percent iron, 0.005 percent sulphur, 0.05 percent silicon, and 0.05percent copper, all by weight.

The cooling fluid employed comprises air, H O (water or steam), or inertgases, such as nitrogen, argon, helium, krypton, xenon, carbon dioxide,or mixtures thereof. Furthermore, the reactants, e.g., metal halide,such as TiCl, or oxygen-containing gas may be passed internally throughthe support tubes such that the tubes are cooled and the reactants arepreheated. The preheated reactant can then feed directly into thereaction chamber, e.g., as illustrated in FIG. 4. Likewise, variousliquid and gaseous nucleating or rutile promoting agents may be employedas a cooling heat transfer fluid, particularly those metals which form awhite oxide, such as silica and alumina. In addition, carbon monoxidemay be circulated as a cooling fluid in place of, in addition to, ormixed with the gases noted above, the CO then being fed into thereaction chamber to be oxidized and to supply heat to the reaction zonefor the sustaining of the reaction. Sulphurcontaining compounds, asdisclosed in copending US. Application Ser. No. 15,300, now US. Pat.3,105,742, may

also be employed. Finally, the cooling fluid may comprise a recyclestream of gases from the reactor chamber, preferably a recycle streamfrom which the metal oxide pigment product, e.g., TiO has beenprecipitated or otherwise removed from the eflluent gas stream, e.g., bymeans of a dust collector or cyclone.

The point or edge of the ceramic arm is located and positioned adjacentto the internal surface of the reactor wall at a distance of inch(one-quarter inch) to 9 inches (nine inches), preferably 4 inches(three-quarters inch) to 2 inches (two inches).

The angle alpha or, as shown in FIGS. 6 and 8, should exceed (ninetydegrees), preferably (one hundred ten degrees) to 145 (one hundredforty-five degrees).

The angle theta 0, as shown in FIGS. 6 and 8, suitably should exceedwhereas the angle phi in FIGS. 6 and 8, suitably should range from 15 to75", preferably 30 to 55.

Where the scraper arms and supports are projected upwardly from thebottom of the reactor, as disclosed in FIG. 1, there is a cantileveraffect such that the portion of the supports near the bottom is undergreater stress than that portion at a greater distance from the bottom.This canilever affect is particularly pronounced where a single arm(with supports) is employed, e.g., FIG. 3.

The cooling fluid is introduced into the system, e.g., via conduit 1 inFIG. 1, at a temperature of 150 F. to 300 F., preferably 200 F. to 250R, such that it exits, e.g., conduit 11 in FIG. 1, at a temperature of200 F. to 500 F. Temperatures below 150 F. tend to cool the reactionzone, whereas temperatures above 300 F. cause the supports to overheat.

Where the cooling fluid is a gas, it suitably is flowed through thesupports at 300 to 900 standard cubic feet per minute calculated at 70F. and one atmosphere (14.7 pounds per square inch absolute) pressure.

Where air is employed as a cooling media in the practice of thisinvention, it has been found that the optimum air flow rate (standardcubic feet per minute) per effective outside cooling area of the metalsupports (square feet) should range from 5 to 10, preferably 6.5 to 8.5.Effective outside cooling area is defined as that external portion ofthe support exposed to the reactor corrosion and thermal conditions,e.g., that portion exposed within the reactor.

Where the length of the arm and supports is long, e.g., in excess of 10feet, the section modulus of at least one support should be graduallyand uniformly increased in a direction toward the reactor bottom in anamount suflicient to withstand and endure the increasing stress.

Where a support is a tubular element with an internal diameter d and anoutside diameter D, the section modulus Z is determined by the formula:

Where the support is an elliptical tube, e.g., conduits 8, 8A, and 8B inFIG. 1, having an outer major radius a, outer minor radius b, innermajor radius 0, minor radius d, the section modulus is determined by thefollowing formula:

In the practice of this invention, it has been found particularlyadvantageous to employ a vapor phase oxidation process wherein aluminumtrichloride (AlCl is added as a nucleating agent to the reaction zone,preferably with the metal halide reactant, e.g., TiCl in an amountsufficient to give a final Ti-O pigment product containing 0.1 to 8percent A1 preferably 1 to 4 percent by weight of the pigment.

When so practicing the invention, the TiO pigment which adheres to thereactor wall surprisingly contains a higher percent by weight of A1 0than the TiO product exiting from the reactor. Thus, whereas the productcontains 1% percent by weight A1 0 the TiO; on the wall surface contains3 to 7 percent, usually about percent, by weight A1 0 The following aretypical working examples.

EXAMPLE I Three ceramic dedusting arms were arranged in a verticalcylindrical reactor, as shown in FIGS. 1 and 2. The

reactor was 14 feet long with an internal diameter of 4 feet; one-sixth/6) of the internal wall was constructed out of brick comprising 45.1percent A1 0 51.9 percent SiO 1.4 percent Fe O 1.7 percent TiO 0.1percent CaO, 0.3 percent Na O, and a trace of MgO, all by weight and theremaining five-sixths /6) was constructed out of brick comprising 40.0percent A1 0 54.6 percent SiO 2.4 percent Fe O 1.2 percent TiO 1.5percent CaO, 0.1 percent MgO, 0.4 percent alkalies, all by weight.

All of the supports for the ceramic arms were constructed out of aNickel 200 consisting of 99.45 percent nickel, 0.06 percent carbon, 0.25percent magnesium, 0.15 percent iron, 0.005 percent sulphur, 0.05percent silicon, and 0.05 percent copper, all by weight.

The supports 4, 5, 4A, 5A, 4B, and 5B, were fabricated out of l-inchSchedule 40 pipe flattened into an ellipse having a major outside axisor diameter of 1% inches (one and one-half inches).

The supports 8, 8A, and 8B were fabricated out of 3 inch Schedule 40pipe flattened into an ellipse having a minor inside axis or diameter of1%; inches (one and nine-sixteenths inches).

The supports 3, 3A, and 3B, were fabricated out of 2-inch Schedule 40pipe flattened into an ellipse having a minor inside axis or diameter ofabout 1% inches (one and one-half inches).

Exit conduit 11 was fabricated out of 8-inch Schedule 40 pipe.

Inlet conduit 1 was fabricated out of 6-inch Schedule 40 pipe.

Tubes 10, 10A, and 10B, were fabricated out of 1%- inch Schedule 40pipe.

Shaft 2 was fabricated out of a 3-inch hot rolled carbon steel and Wasconnected to a 7.5 horsepower motor by means of a belt drive, the motorbeing designed to rotate the shaft 2 and the ceramic arms at threerevolutions per minute.

The ceramic arms 6, 6A, and 6B, were constructed out of a steatiteproduct of talc, 3MgO-4SiO -H O. Angles theta 0, and phi 5, wererespectively about 135 (one hundred thirty-five degrees) and 30 (thirtydegrees). Angle alpha or, was in excess of 90 (ninety degrees).

At the top of the reactor, three concentric tubes were arranged as shownin FIG. 11, 38 gram-moles per minute of oxygen at 1150 C. beingcontinuously fed through tube 124 having an internal diameter of fourinches while 32 gram-moles per minute of titanium tetrachloride at 525C. were continuously fed through tube 128 into annulus 130 having amaximum diameter of 12 inches. Chlorine at 400 C. was continuously fedat a rate of 5 to 7 gram-moles per minute into annulus 129 having amaximum diameter of seven inches.

Sixty to 130 grams per minute of vaporous aluminum trichloride at 300 C.were introduced into the TiCl stream before it was fed into annulus 130.Liquid silicon tetrachloride at the rate of 0.19 gram-mole per minutewas also added to the TiCl before the introduction of the TiCl into theannulus.

As the three ceramic arms were rotated at three revolutions per minutealong the internal wall surface of the reactor, air was circulated byblower means through the supports at the rate of 550 standard cubic feetper minute calculated at F. and 1 atmosphere (14.7 pounds per squareinch absolute). The air was fed into conduit 1 at 225 F. and 13.5 poundsper square inch gage. The exit temperature of the air stream to theatmosphere from conduit 11 was 375 F., the pressure drop of the airstream through the system being 13.5 pounds per square inch.

The design air velocity through each support 4, 5, 4A, 5A, 4B, and 5B,was 129 feet per second. The design air velocity through each support 8,8A, 8B was 113 feet per second. The calculated air flow rate pereffective cooling area of the supports was 7. standard cubic feet of airat 70 F. and one atmosphere per square foot of eflective externalcooling area for the supports.

The process was operated continuously in excess of 168 hours andintermitently in excess of 1440 hours without any plugging of thereactor. During this time, the metal oxide removed from the reactorwalls analyzed at 3 to 6 percent by weight A1 By comparison, thepigmentary TiO product exiting from or near the reactor bottom containedto 2 percent by weight A1 0 The product was then wet finished and coatedwith 0.01 to 8 percent by weight silica, 0.1 to 4 percent by weight Ti0and 0.05 to percent by weight A1 0 (all basis the weight of the pigment)in an acid pH media using the procedure set forth in the copending US.application Ser. No. 121,327, filed July 3, 1961, by Dr. Hartien S.Ritter, now US. Letters Patent 3,146,119.

A typical pigment product after wet coating had a tinting strength inexcess of 1720 on the Reynolds scale as determined in accordance withA.S.T.M. D33226, (1949 Book of A.S.T.M. Standards, part 4, p 31,published by the American Society for Testing Materials, Philadelphia,Pa.

EXAMPLE II The procedure, as set forth in Example I, was followed,except that the ceramic arms and nickel supports were removed from thereactor. In other words, the vapor phase TiO oxidation was operated notin accordance with this invention.

The reactor was operated continuously for 24 hours at which time TiObuildup on the internal surface of the reactor plugged the reactor. Atypical pigment product after wet coating had a tinting strength on theReynolds scale below 1650.

EXAMPLE III The procedure, as set forth in Example I, was followed,except that no ceramic arms were employed. Instead, a rotatingair-cooled nickel alloy edge was used. The device was operatedintermittently for 192 hours out of 360 hours, at which time itstructurally failed due to abrasion and heat stress. In addition, thenickel edge tended to compact the metal oxide onto the surface of thewall and did not satisfactorily remove it.

Although this invention has been described with particular reference totitanium tetrahalide, e.g., titanium tetrachloride, titaniumtetrabromide, and titanium tetraiodide, it may be used in the productionof other pigmentary metal oxides.

The term metal, as employed herein, is defined as including thoseelements exhibiting metal-like properties, including the metalloids.Examples, not by way of limitation, but by way of illustration ofpigmentary metal oxides which may be produced by the aforementionedprocess, are the oxides of aluminum, arsenic, beryllium, boron,gadolinium, germanium, hafnium, lanthanum, iron, phosphorus, samarium,scandium, silicon, strontium, tantalum, tellurium, terbium, thorium,thulium, tin, titanium, yttrium, ytterbium, Zinc, zirconium, niobium,gallium, antimony, lead, and mercury.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings, and will be obvious to oneskilled in the art. Thus, it will be understood that the invention is inno way to be limited except as set forth in the following claims.

We claim:

1. An apparatus for removing metal oxide from the wall of a reactorchamber having a centrally disposed longitudinal axis comprising:

(a) at least one elongated ceramic edge in brushing contact with metaloxide on said wall, said edge extending substantially parallel to saidwall in the direction of said longitudinal axis;

(b) support means extending along each ceramic edge for supporting saidedge in brushing contact with said metal oxide;

(c) means for moving said support means and thus said ceramic edgeacross said metal oxide on said wall;

(d) conduit means disposed adjacent to and extending externally alongsaid support means; and

(e) means for supplying coolant to said conduit means to cool saidsupport means.

2. An apparatus for removing metal oxide growth from the internal wallof a vertically disposed vapor phase oxidation reaction chambercomprising:

(a) at least one elongated ceramic edge in brushing contact with metaloxide on said wall, said edge being disposed in a substantially verticalplane;

(b) conduit means extending in a substantially vertical plane andsubstantially from top to bottom within said reactor chamber, saidconduit means including at least two substantially horizontally disposedand vertically spaced hollow metal members for supportmg each ceramicedge at a predetermined distance from the vertically extending portionof said conduit means and from said wall, said horizontally disposedhollow metal members being in fluid communication with said verticallyextending portion of said conduit means;

(0) rieans for supplying coolant to said conduit means;

(d) means for moving said conduit means and thus saiill ceramic edgealong said metal oxide on said wa 3. An apparatus for removing metaloxide accumulatron from the internal wall of a titanium tetrahalidevapor phase oxidation chamber, said chamber having a centrally disposedlongitudinal axis comprising:

(a) at least one ceramic arm having a blade-like ceramrc edge extendingsubstantially longitudinally along and adjacent to, but spaced from,said wall;

(b) first substantially longitudinally extending conduit means formaintaining each arm a predetermined distance from said longitudinalaxis and said wall;

(c) second substantially longitudinally extending conduit means disposedadjacent and external relative to said first conduit means for receivingcooling fluid to thereby cool said first conduit means; and

(d) means for moving each ceramic arm along the metal oxide accumulatedon said wall.

4. An apparatus for removing metal oxide growth from the internal wallof a cylindrical reactor wherein titanium dloxide is produced by vaporphase oxidation of titanium tetrahalide comprising:

(a) at least one ceramic arm having a blade-like edge positionedadjacent to, but spaced from, the surface of the wall and beingsubstantially parallel to the Wall, said edge being elongated in thedirection of the axis of said cylindrical reactor;

(b) metal support members extending along each arm for supporting eachblade-like edge in brushing con tact with said metal oxide;

(c) conduit means disposed adjacent and external relative to saidsupport members and extending along substantially the entire lengththereof;

(d) means for supplying cooling fluid to said conduit means to cool saidsupport members; and

(e) means for rotatively moving each ceramic arm and support members ina path concentric to the wall.

5. The apparatus of claim 4 wherein each edge is positioned at adistance of 0.75 to 2.0 inches from the wall.

6. The apparatus of claim 4 wherein each edge is slanted at an anglegreater than with respect to a tangent to the circular path.

7. The apparatus of claim 4 wherein each support member is constructedout of a nickel alloy.

8. The apparatus of claim 4 wherein the cooling fluid 1s air.

9. The apparatus of claim 8 wherein the air is flowed at a rate of 6.5to 8.5 standard cubic feet per minute per square foot of eflectiveoutside cooling area of each support member.

10. The apparatus of claim 4 wherein the ceramic edge has athermoconductivity of less than 25 B.t.u./ (hour), (square foot),F./inch).

11. The apparatus of claim 4 wherein the ceramic arm has suflicientresistance to a corrosive environment, a thermal conductivity of lessthan 210 B.t.u./ (hour), (square foot), F./inch), and a Mohs hardness ofat least 5.

12. An apparatus for removing metal oxide from the internal wall of areactor chamber having a centrally disposed longitudinal axiscomprising:

(a) a shaft extending along said longitudinal axis and into saidchamber;

(b) support means mounted to said shaft and disposed within saidchamber, said support means having a longitudinally extending surfacedisposed a predetermined distance from said wall;

(c) at least one longitudinally extending brushing member mounted tosaid support means, said brushing member having a longitudinallydisposed ceramic edge in brushing contact with metal oxide on said wall;

(d) conduit means disposed adjacent and external rela- 12 tive to saidsupport means and extending along said longitudinally extending surfacethereof;

(e) means for supplying a coolant to said conduit means, said conduitmeans thereby cooling said support means; and

(f) means for rotating said shaft, thereby moving said edge across saidmetal oxide on said wall.

13. Apparatus according to claim 12 wherein said reaction chamber issubstantially cylindrical and said means for rotating said shaft ismotor means.

14. Apparatus according to claim 13 wherein said reaction chamber is forthe vapor phase oxidation of titanium tetrachloride and said ceramic armhas sufficient resistance to a corrosive environment, a thermalconductivity of less than 210 Btu/(hour), (square foot), F./inch), and aMohs hardness of at least 5.

References Cited UNITED STATES PATENTS 2,805,921 9/1957 Schaumann23-202V 2,869,311 1/1959 Beeston, Jr. 30--35OX 2,979,414 4/1961Ryshkewitch 106-44 ROBERT W. MICHELL, Primary Examiner US. Cl. X.R.23-277, 293

